Consequently, in Table 5 in the column “Region” for substance 5 “A/B” changes to “A”. “
“In a typical 2D homonuclear correlated spectrum the diagonal contains the most intense peaks, although all the relevant information is contained in the cross peaks. These intense signals can obscure nearby cross peaks. Furthermore, the diagonal is often responsible for the so called t1-noise, artifacts along the indirect dimension. Intense diagonal peaks learn more also limit the dynamic range of the spectrometer, leading to a lower sensitivity of low intensity signals. The stronger the diagonal peaks in relation to the cross peaks are, the bigger

are the problems they cause. In particular, NOESY-type spectra, where the intensity ratio of diagonal versus cross peaks is quite extreme, often suffer from strong diagonal peak artifacts which can easily obscure nearby cross peaks. Several different strategies for diagonal peak suppression have been reported in the literature. The first approach is based

on suppressing diagonal peaks by recording two spectra, a regular 2D spectrum and one containing only the diagonal [1] and [2]. The latter is obtained by setting the mixing time to zero. Subtraction of the diagonal-only spectrum from the regular one provides a diagonal-free spectrum. However, this approach only works if there is no significant relaxation during the mixing time and does not alleviate the t1-noise or dynamic range problem since one still has to record datasets with a diagonal. In addition, by using PFT�� this technique, the acquisition of two different comparable spectra requires a high accuracy of the parameter settings. Otherwise subtraction artifacts will lead to insufficient suppression of the diagonal

[2], [3] and [4]. The second method destroys the magnetization of the excited nucleus by a defocus, mixing, refocus sequence [5]. The mixing period is implemented between two 90° pulses. The magnetization of the excited nucleus, which has not been transferred during the mixing period, undergoes a 180° rotation. A last 90° pulse transfers this magnetization Oxymatrine into the z-direction leading to no visible signal of the diagonal in the spectrum. This method leads to an unusual appearance of the 2D spectra, showing cross peaks on diagonals with a slope Δω1/Δω2 = 2. Another method, which has been used to suppress diagonal peaks in a NOESY spectrum uses a combination of two jump-and-return sequences before and after the mixing and a pulsed field gradient to suppress magnetization that evolved with the same frequencies before and after mixing [6]. By this approach the signal intensities in the 2D spectrum are modulated by a sheared sinusoidal profile with zero intensity on the diagonal as a result of the jump-and-return sequences.